Bump virtualenv from 20.14.1 to 20.15.0 in /.github/workflows

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.14.1 to 20.15.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.14.1...20.15.0)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -5,4 +5,4 @@ nox==2022.1.7
 nox-poetry==1.0.0
 poetry==1.1.13
 pre-commit==2.19.0
-virtualenv==20.14.1
+virtualenv==20.15.0